There is a continuing need for alloys to enable disk rotors in gas turbine engines, such as those in the high pressure compressors and turbines, to operate at higher compressor outlet temperatures and faster shaft speeds. The higher temperatures and increased shaft speeds facilitate the high climb rates that are increasingly required by commercial airlines to move aircraft more quickly to altitude, to reduce fuel burn and to clear the busy air spaces around airports. These operating conditions give rise to fatigue cycles with long dwell periods at elevated temperatures, in which oxidation and time dependent deformation can significantly decrease resistance to low cycle fatigue. As a result, there is a need to improve the resistance of alloys to surface environmental damage and dwell fatigue crack growth, and to increase proof strength, without compromising their other mechanical and physical properties or increasing their density.
Conventional high pressure compressor disks and/or high pressure turbine disks of gas turbine engines are often produced from high strength nickel-base superalloys. These materials are often highly alloyed with refractory elements to enhance strength and precipitate a high volume fraction of gamma prime strengthening phase into the gamma phase. The grain structure of such alloys is typically designed to optimize strength and low cycle fatigue performance and/or resistance to fatigue crack growth and creep deformation by controlling heat treat parameters. Examples of highly alloyed nickel-base superalloys are discussed in U.S. Pat. No. 6,132,527; U.S. Pat. No. 6,521,175; and U.S. Pat. No. 6,969,431. As the overall level of refractory alloying elements increases in such alloys, the microstructure can become thermodynamically unstable, such that microstructural changes occurring during operation can reduce mechanical properties of the alloys.
Future gas turbine engine components likely will be required to operate at higher temperatures and/or higher stresses than existing ones. Presently available nickel-base superalloys may be unable to meet these future operating requirements. Various alloys have emerged as potential candidates for future gas turbine engine turbine and/or compressor disks. Examples of such alloys, which typically employ third phase precipitation of delta or eta phase to enhance high temperature mechanical properties, are discussed in U.S. Patent Application Publication No. 2012/0027607 A1; U.S. Pat. No. 8,147,749; U.S. Patent Application Publication No. 2013/0052077 A1 and U.S. Patent Application Publication No. 2009/0136381 A1. However, the strength, stability or ductility of some of these materials may not be adequate for the high stresses and highly multi-axial stress states encountered by compressor and turbine disks in operation and the high tantalum content, a heavy and expensive element, in some of the alloys could adversely affect cost and density. Additionally, decohesion at the interface of the matrix and third phase precipitates during high temperature thermomechanical processing or during service operation could cause premature failure of the highly stressed rotating components.